New nidus formation adjacent to the target site of an arteriovenous malformation treated by Gamma Knife surgery Report of 3 cases

New nidi are rarely found adjacent to the resection margin following treatment for an arteriovenous malformation (AVM), especially in adults. In addition, there are no reports in adults of new nidus formation adjacent to the targeted site of an AVM that angiography has verified to be completely obliterated by radiosurgery. The authors present their experience with recurrent AVMs following AVM radiosurgery in 3 patients whose ages were 9 years, 10 years, and 33 years. None of the patients had been treated with embolization before radiosurgery. Two patients had a history of intracerebral hemorrhage before radiosurgery. New lesions developed around the obliterated nidi in all 3 cases. Angiography performed after the first radiosurgery confirmed complete removal of the nidus in all 3 patients, and new nidus formation was detected 31,132, and 36 months after the initial GKS. The new lesions were also treated by GKS. Occasionally, in patients with recurrent AVMs, such as those described in this paper, long-term clinical and angiographic follow-up may be required, even if complete occlusion is originally shown on angiograms. (http://thejns.org/doi/abs/10.3171/2012.8.GKS12994)